1. Field of the Invention
The present invention relates to repeatable timing error correction systems and methods. More particularly, the present invention relates to repeatable timing error correction systems and methods for use with a servo writer.
2. Description of the Prior Art and Related Information
Computer systems often rely on disk drives for storing and retrieving data. Disk drives typically employ a moveable head actuator to frequently access large amounts of data stored on a disk. One example of a disk drive is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the moveable transducer head over a particular track on the disk to write or read information to or from that track, respectively.
Typically, a conventional hard disk drive includes a disk having a plurality of concentric tracks. Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information may be provided on each disk to determine the position of the moveable transducer head by a servo control system of the disk drive.
The most popular form of servo control is “embedded servo” wherein the servo information is written in a plurality of servo sectors that are angularly spaced from one another and that are interspersed between data sectors around each track of each disk.
When manufacturing a disk drive, servo sectors 20–2N are written to a disk 4 in order to define a plurality of evenly-spaced, concentric data tracks 6, as shown in the prior art disk format of FIG. 1. Each servo sector (e.g., servo sector 24) includes a preamble 8 for synchronizing gain control and timing recovery, a sync mark 10 for synchronizing to a data field 12 comprising coarse head positioning information such as a track number, and servo bursts 14 which provide fine head positioning information. During normal operation, the servo bursts 14 are processed by the servo control system of the disk drive in order to maintain the head over a centerline of a target track while writing or reading data.
Servo writers may be used to write the servo sectors 20–2N to the disk surface during manufacturing. Servo writers may employ extremely accurate head positioning mechanics, such as laser interferometers or optical encoders, to ensure that the servo sectors 20–2N are written at the proper radial location from the outer diameter of the disk to the inner diameter of the disk. In addition, extremely accurate clocking systems are necessary in order to write the servo sectors in the proper circumferential locations 20–2N on the disk.
Unfortunately, conventional clocking systems utilized in servo writers often impart repeatable timing errors into the servo writing process such that servo sectors (e.g. 20–2N) are written to the disk in a manner that incorporates the repeatable timing errors of the clocking system. This results in poor accuracy in the location of the servo sectors written onto the disk, which can result in poor tracking behavior of the disk drive servo system, and a lower data capacity than may otherwise be achieved. Eccentricity associated with the servo sectors results in timing uncertainties being introduced into the servo control system and resultant servo control signals. When this eccentricity occurs, the servo sectors appear to the servo control system of the disk drive as if they are not evenly spaced such that timing uncertainties are introduced into the servo control system causing problems in both the reading and writing of data.
Thus, servo writers that write servo sectors and servo information to disks need an accurate clock source. However, as previously discussed, conventional clock systems typically used in the servo writing process may be subject to repeatable timing errors. Unfortunately, these repeatable timing errors are incorporated into the written servo sectors resulting in degraded disk drive performance and lower data capacity.